There is a big difference.

When a criminal case is expunged, all records of that arrest and subsequent court proceedings are destroyed. The court’s records are destroyed, the district attorney’s records are destroyed, the police’s records are destroyed, the jail’s records are destroyed, and the case is erased from the state’s criminal history database. It is as if the criminal case never happened.

When a criminal case is nondisclosed, the records aren’t destroyed but instead sealed from public view. The court, the district attorney’s office, the police, and the jail keep the records but are ordered not to disclose the existence of the case (hence the term, nondisclosure) to anyone except other law enforcement agencies and the government. If a government agency or police department runs a background check, they will be able to see the record of the case but private employers will not.